AutoStart - Shutdown Charger/Generator

 

Greetings,
I have a single battery on a trailer that I would like to find a way to
charge when it runs down. Cutting Grass one day, I started to think
about an older Lawn mower I had with a Vertical Shaft engine and a belt
drive "starter/generator" on it.

After a little research, I find out that the Generator part on most of
those puts out 15amps, with Golf Cart units up to 25 amps. So I easily
can envision that with a simple circuit even I could wing together,
this thing could autostart when the voltage drops to a certain point.
What I do not know how to do is build a circuit that can shut the thing
down when the time is right. Easiest for me would be a timer circuit,
but that would not be as accurate as something that monitored the
battery.

With all of you fellows who are familiar with proper charging
techniques, is it possible to build some sort of monitor circuit that
could ignore the fact that there would be a full 12v in the system the
minute it starts and runs, but charges or runs long enough to charge
things correctly and then shuts itself down ?

I would think that those 15 amp starter/generators wouldn't take much
more than one horse or so to pull, and I would like to have the
smallest most compact motor possible. However, today, there is not too
much on the shelf in a 4 stroke with an automatic choke under 4hp, so
that is what I would likely end up with.

Any pointers appreciated,

Grummy

 

On 4 Aug 2005 20:23:03 -0700, grumtac@sbcglobal.net wrote:


Depending on your battery, it won't be fully charged at 12V.

In my RE system, the generator autostarts after it has been at some low
voltage for some length of time (e.g. 11.8V for 2 hrs), runs until the
voltage reaches a certain level (e.g. 14.7V); maintains that voltage for a
few hours (for "absorption") and then shuts down.


-- ron  (off the grid in Downeast Maine)

 


Ron Rosenfeld wrote:


I should have indicated a higher voltage. I would assume that those
units do put out more than 12V. After all, those start on demand Golf
carts routinely deliver industrial type service. I will have to throw a
meter on one and see.


H'mmm. I could put a simple countdown timer into place to do that, but
a countdown timer wouldn't take into account any excessive draw on the
battery, unless of course I put another stage in that start logic. I
could make it absolutely start at a lower voltage yet than where the
countdown timer starts.  I wonder why it waits for so long ?


voltage for a

I'm thinking that this "absortion" is actually read or calculated from
somewhere rather than a timer function. My thoughts were something that
checks specific gravity or something ? Is there some kind of probe out
there that can go into a battery cell and be used for anything I am
trying to do ?

Thanks,

Grummy

 

On 5 Aug 2005 05:31:47 -0700, grumtac@sbcglobal.net wrote:


My system actually has multiple parameters for starting the generator:

Below V1 for 24 hours or
  below V2 for 2 hours or
    below V3 for 15 minutes or
      below V4 for 30 seconds or
Load current greater than X amps for Y minutes or
Generator has not run for Z days.

In almost five years, the starting (other than for the "not run" parameter)
has been due to either the V2 or V3 parameter.  Depending on your set up,
you should be able to find a voltage/time combination or two that works for
your system.


voltage for a

One issue is that the rate of charging to get from 80-85% state of charge
(SOC) to 100% SOC can be quite slow.  You can boost the voltage and current
to allow higher levels, but if you do, you run the risk of permanent damage
to your batteries.  It is a good idea to overcharge from time to time (this
is called equalization).  But you have to monitor the battery temperature
and also ensure that you replace the water that will evaporate.

In my RE system, most of the energy comes from wind or PV.  However, when I
run the generator, the settings that I use are designed to only bring the
batteries to about a 75% SOC.  It's too inefficient to run a propane
generator to bring them to 100% SOC, so I ensure that the wind and PV do
that.

I know there are electronic specific gravity testers, but I believe they
are quite expensive.  If you don't want to use time, and you are using a
voltage controlled charger, you could look at charging current, and stop
your generator when it reaches some level for some length of time.


-- ron  (off the grid in Downeast Maine)

 



This is outside of my life's experiences (and I ain't young).  You mean to
say you have a lawnmower with a belt-drive electric start that also doubles
as a generator?  Sounds like what a lot of folks have been building from
scratch to charge batteries.  Got any pictures of it?

Anyway, I would think a circuit that grounds the ignition when it gets to a
specific voltage would be simple to build but as Ron Rosenfeld pointed out
you would probably be better off with something that detects the charge rate
and slows down when it gets to somewhere around half of your maximum charge
rate.  My experience tells me that an older battery might be fully charged
at a lower voltage than a newer battery and the charge rate on volts can
vary with the type of charger you are using.  What I did to avoid all of
this figgering and wondering was to connect an engine driving an alternator
to a battery with an inverter and then I connected my Vector Smart Charger
and use it to do all the thinking for me.  Sounds kinda redundant to use a
battery and an inverter to charge another battery but it works and it's
easy.  Some day I'll figure out how to take the first battery out of the
system but when I tried it the voltage went to high and exploded an
inverter.